1. Technical Field
This description generally relates to the field of wireless identification, and more particularly to wirelessly marking media.
2. Description of the Related Art
Wireless communication devices, including wireless memory devices for storing and retrieving data, such as radio frequency identification (“RFID”) tags, are used in a variety of environments. Such devices typically employ an antenna structure coupled to a wireless transponder circuit to transmit and/or receive data via electromagnetic signals in some frequency range.
Antenna structures may include a primary antenna element driven by a transmitter to transmit data in an outgoing signal and/or driven by an external signal from an external source to receive incoming data. Antenna structures may further include parasitic antenna elements that electromagnetically cooperate with the driven antenna element to enhance the transmission or reception of a signal. Parasitic antenna elements may be chosen from a variety of directors and reflectors, the directors being generally shorter and the reflectors being generally longer than the driven antenna element. The parasitic antenna elements are normally aligned with and are carefully spaced from the driven antenna element and one another.
The wireless transponder circuit found in many wireless memory devices typically includes a memory portion and a logic portion. The memory portion stores data, while the logic portion controls the reading, writing, and manipulating of data in the memory portion. The logic portion may further couple between the memory portion and the antenna to act as a transmitter, receiver, or transceiver for reading and/or writing data to and/or from the wireless memory device.
Active wireless memory devices include a discrete consumable power source, such as a battery, to provide power to the wireless transponder circuit. In contrast, passive wireless memory devices derive power from a wireless interrogation signal, for example, by backscattering the signal as a response signal encoded with information from the wireless memory device. Wireless memory device may be associated with a variety of sensors to measure environmental conditions, such as current or maximum values of pressure, temperature, acceleration, etc.
Wireless marking may be used in a variety of fields to track a high volume of items. For example, in an office environment, it may be desirable to use wireless communication devices to track the large number of documents generated.